This invention relates to the field of electric discharge machining (EDM), and provides a device for holding a graphite electrode used in an EDM device.
Electric discharge machining (EDM) is a process used for machining steel. An electric arc, extending from a graphite electrode to the steel surface being machined, erodes away the steel by locally liquefying and cooling the steel, in the presence of a dielectric fluid. The key component in this process is the graphite electrode, which must be reliably supported and accurately positioned to provide a precisely machined product. Since the shape of the electrode determines the shape of the cavity formed during the EDM process, it is especially important to position the electrode accurately.
Various methods of holding the graphite electrode have been used in the prior art. It has been known, for example, to provide a holding device which grasps the electrode with a setscrew. Other methods use glue to attach the graphite to an electrode holder. Examples of holders for electrodes used in EDM are shown in U.S. Pat. Nos. 4,713,515 and 4,717,803, the disclosures of which are hereby incorporated by reference.
The electrode holding devices of the prior art generally have the disadvantage that they cannot be easily used with electrodes of widely varying sizes. Since graphite electrodes are relatively expensive, it is common to retain the unconsumed remnants of such electrodes after an EDM job is completed, for later use on another job. But using such remnants is often problematic because of their irregular size. To use a partially-consumed electrode efficiently, it is necessary to position the electrode properly relative to the workpiece.
The present invention provides a device which can conveniently and accurately hold electrodes of various sizes. The invention includes means for automatically maintaining the electrode on a desired center line, regardless of the size or shape of the electrode.